length calculation problem(s) - General - Punch! CAD

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#1
Posted
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Friday, March 22, 2019 7:58:12 PM(UTC)

Rank: Senior Member

Joined: 1/16/2015(UTC) Posts: 295

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most of the time SharkCAD Pro and ViaCAD 7 provide length answers to ±0.000001" without problem. that said, there have been infrequent cases dating back to my ViaCAD 7 days where getting length answers to ±0.001" have been a struggle!! problems have not happened frequently enough for me to recognize the boundary conditions that lead to marginal or unusable answers. the first attached chart shows the overall context of the one variable graphical construction; the variable distance from an arbitrary point keys the construction establishing the plane of the first bend. the second attached chart shows the key elements of the construction in greater detail; the first bend radius equals 2.50" and the second bend radius at 3.00". the construction starts with a 5" diameter (D = 2 x R)circle at a point 0.75" from the beginning of the tube in the plane established by the variable point. a second 5" circle at the quadrant point of the first locates the bend. a tangent from the variable point to the tangent to the second circle establishes the extent of the first bend. an arc drawn about the center of the second circle from the tangent to the second circle to the center of the first circle defines the bend; creating a line from the center of the first circle to the starting point and joining it to the arc is convenient at this point. the next step is creating a new working plane using the variable point, the end point, and the tangent to the second circle. a 6.00" diameter circle (ie: D = 2 x R) is drawn tangent to the lines connecting the variable point to the end point AND the tangent to the second circle. two lines are drawn from the center of the 6" circle to the two tangent points and an arc drawn between the two tangent points. after a line is drawn between the tangent point and the end and the other tangent point and the tangent point to the second circle, the lines and arcs are jointed to create a single object. the verify tool provides the length of the resulting object.

length being a continuous function for the described geometry, time (ie: iterations) should be the only consideration with regard to the precision of the answer being sought. the third attached chart shows the lack of convergence AND linearity for my latest encounter with the calculation problem(s) !!! it's my sense one of the components in the calculation chain has a small error that becomes unstable under certain undefined conditions. to that end I've attached a copy of the layer/tube with the problem in the hopes that the problem(s) can finally be identified and fixed.

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